Can't stage file with Merge Changes via `workbench.action.git.stage`

- VSCode Version: 1.6.1
- OS Version: Linux 4.7.7-200.fc24.x86_64

Steps to Reproduce:
1. Run something like `git stash pop` which results in a conflict.
2. Open the conflicted file.
3. Press keybinding for `workbench.action.git.stage` to stage it.
4. Nothing happens. Clicking the + button by hand works though.
